1. Field of the Invention
The present invention relates to an active matrix liquid crystal display device.
2. Description of the Related Art
In a word processor, a personal computer, a portable TV and the like, a thin and lightweight display device is widely used. Particularly, since it is easy to realize a thin and lightweight liquid crystal display device with low power consumption, there has been extensive development of the liquid crystal display device. Accordingly, a liquid crystal display device with high resolution and a large-sized screen has been available at a relatively low price.
Among the liquid crystal display devices, an active matrix liquid crystal display device, in which thin film transistors (TFTs) are disposed at respective intersections between a plurality of signal lines and a plurality of scan lines, is excellent in color reproduction and has fewer afterimages. Thus, it is considered that the active matrix liquid crystal display device will become mainstream in the future.
In a conventional active matrix liquid crystal display device, drive circuits which drive signal lines and scan lines are formed on a substrate different from an array substrate having the signal lines and the scan lines disposed thereon. Thus, it was impossible to miniaturize the whole liquid crystal display device. Consequently, there has been extensive development of a manufacturing process of integrally forming the drive circuits on the array substrate.
In a liquid crystal display device using amorphous silicon TFTs, drive ICs (integrated circuits), on which TCPs (tape carrier packages) are mounted by use of a TAB (tape automated bonding) method, supply video signals to signal lines from outside an array substrate. However, along with realization of high definition pixels, the number of connection wirings on the array substrate for connecting the drive ICs to the array substrate is increased. Thus, it is difficult to secure a sufficient pitch between these connection wirings.
Meanwhile, in a liquid crystal display device using polysilicon TFTs, a scan line drive circuit and a signal line drive circuit can be integrally formed on an array substrate. Thus, the number of external connection parts can be reduced. Moreover, cost reduction and reduction in the number of connection wirings can be achieved. As a technology of realizing the cost reduction by further reducing the number of external connection parts, for example, there is signal line selective drive described in Japanese Patent Laid-Open Publication No. 2001-312255. This technology is intended to reduce the scale of drive ICs in such a manner that the number of video output lines extended from the drive ICs is reduced to half, each of the video output lines is allowed to correspond to two signal lines on an array substrate and any one of the two signal lines is selectively switched and connected to the video output line.
Moreover, as a method for driving signal lines which write video signals into pixels, a V line inversion drive method and a H/V inversion drive method are known. In the V line inversion drive method, polarities of video signals supplied to signal lines for each vertical scan period are switched between positive and negative and video signals having inverted polarities are supplied to adjacent signal lines. In the H/V line inversion drive method, polarities of video signals supplied to signal lines for each horizontal scan period are switched between positive and negative and video signals having inverted polarities are supplied to adjacent signal lines.
However, when the V line inversion drive method is applied to the signal line selective drive, there is a deviation caused in a distribution of polarities for entire pixels. Thus, there is a problem that display failure called a crosstalk, which has a tail along a window pattern in displaying the window pattern, is likely to occur.
Moreover, when the H/V inversion drive method is applied to the signal line selective drive, since an inversion cycle of video signals is short, in addition to a conventional problem such as increased power consumption, there is the following problem. Specifically, in half-tone raster display, when a video signal is supplied to a selected signal line, the video signal changes a potential of an adjacent signal line in a floating state through coupling capacities between its own pixel and its own signal line, between its own pixel and an adjacent signal line and between its own signal line and the adjacent signal line, respectively. Thus, there is a problem that there occurs a difference in write potentials into pixels for each signal line and uneven display occurs.